Energetic particle experiment DOK-2

Introduction

The study of energetic particles acceleration and transport within the magnetosphere and on its boundaries is the main goal of DOK-2 experiment on Auroral Probe in a frame of INTERBALL project. Two particle spectrometers: DOK-2 and its small version - DOK-2S were installed on the main satellite and small subsatellite. Both function successfully since launch on 29 August, 1996. DOK-2 experiments on Tail and Auroral Probes of INTERBALL project continue our studies of energetic particle population on Prognoz 10 satellite in 1985 (Intershock project). Due to much higher energy, angular and time resolution, better separation of electrons and ions it is expected that DOK-2 experiment will allow to re-examine in more details energetic particle population and related processes in magnetosphere regions covered by the spacecraft orbit.

DOK-2 spectrometer

DOK-2 uses two pairs of energetic particle telescopes. Each telescope has a single, passively cooled, totally depleted, surface-barrier silicon detector. One detector of each pair (1e, 2e) is of 0.3 mm thick. Thin foil in front of detector protons with energies E < 400 keV so this detector measures electron spectrum in 20 - 420 keV range. The second detector (1p, 2p) of 0.15 mm thick is supplied with a broom magnet, deflecting electrons up to 1500 keV. It measures spectrum of ions (protons) in 20-850 keV range. Full aperture angles and geometric factors of electron telescopes are of 27^o and 0.066 sm²*sr. For proton telescopes these values are 12.7^o and 0.015 sm²*sr . Particle flux angular distribution is measured using spacecraft rotation with a 2 min period around the axis directed to the Sun (the angle ) and mechanical scanning of the second telescope pair in a plane containing the rotation axis (the angle ). So 3-dimensional particle distribution function is measured during each 2 min rotation period. About seven full scanning cycles are carried out for every rotation. The first detector pair (1e, 1p) is fixed in the antisolar direction. Moving detector pair (2e, 2p) can either scan from =45^o to 180^o (to a Sun direction) or stay in one of 4 positions: 45^o, 90^o, 135^o and 180^o.

Analogue electronics for each of 4 detectors consists of a charge sensitive preamplifier (in a cooled part of the instrument), a shaping pulse amplifier and 56-57 channel amplitude analyser AA (logarithmic ADC). The measurements base is formed of "elementary measurement" (EM) - one full 56-57 channel spectrum measured every 1 sec for each of 4 telescopes. This information is available only during the most informative Real Time mode of DOK-2. In storing modes there are two kinds of output information formed from EM's :

• Full 56-57 channel spectra accumulated during time intervals from 10 s to 1464 s depending on a particle intensity.
• Three time profile (TP) parameters for each detector. TP-parameters are counting rates in 3 narrow (<30%) energy intervals. Energy values of TP-parameters are shown in Table 1. An accumulation time for TP is variable in basic Monitoring modes (1-260 s). It depends on variability of particle intensities. Special algorithm ensures time resolution of 1 s when intensity change is statistically valuable. In Fast modes accumulation time interval is <1 s.

The mechanical scanning occurs only in Fast and Real Time modes. Transition from Monitoring to more informative Fast modes occurs automatically when particle flux variability is high enough or after a sharp increase of fluxes. Return to Monitoring mode is also automatic.

Telescope	Energy values, keV			Angle, deg
	TP1	TP2	TP3
1e	21-26	39-48	76-95	180
2e	20-24	37-46	73-92	45-180
1p	22-28	46-60	101-132	180
2p	21-27	45-59	101-133	45-180

Experiment status

Spectrometer DOK-2 was switched on 5 hours after the launch on 29.08.1996 and is in a continuous operation up today. Tests of the instrument on 3.09.1996 showed normal function of all. As for Tail Probe some problems were with moving telescope mechanics. 2e and 2p-telescopes stay at =79^o. All other systems both hardware and software are working normally.

DOK-2 data are processed at the Space Research Institute RAS, at the Institute of Experimental Physics SAS and at the Demokritos University of Thrace, Greece. DOK-2S data are processed at the Institute of Experimental Physics.

Examples of DOK-2 data.

Figures 1-7 show some examples of DOK-2 data for 1 hour time interval corresponding to the Auroral zone boundary intersection on 3.09.1996 11.00-12.00 UT. For this time interval:

ALT

=19169-17048 km,

ILAT

=75.5-68.6^o,

MLT

=11.30-12.20

Fig.1	Fig.2	Fig.3	Fig.4
Fig.6	Fig.7	Fig.1

V.N. Lutsenko,

Space Research Institute, Russian Acad. of Sci., Profsojuznaja 84/32, 117810 Moscow, Russia.

K. Kudela (PI),

Institute of Experimental Physics, Slovak Acad. of Sci., Watsonowa 47 04353 Kosice, Slovakia.

E.T. Sarris,

Demokritos University of Thrace, Department of Electrical Engineering, 67100 Xanthi, Greece.

Correspondence to: V.N. Lutsenko. Phone: 7-095- 333-33-56, Fax: 7-095-310-70-23, E-mail: vlutsenk@volt.iki.rssi.ru